1. Field of the Invention
The present invention relates to an identification system utilizing a portable passive tag which is powered by and communicates with a stationary reading device. More particularly, the present invention relates to an identification system and method in which the portable tag communicates with the reading device by magnetic coupling.
2. Description of Related Art
Portable passive security tag systems have been proposed that use magnetic coupling for energy transfer from a stationary power source to a credit card size portable uniquely coded security tag.
In such systems, a transmit coil of a reader creates a magnetic field which alternates at a frequency, typically below 200 KHz. The magnetic field of the transmit coil induces current flow in a portable tag and thereby produces a voltage. The portable tag rectifies the voltage to provide a voltage sufficient to power an application specific integrated circuit (ASIC) which is part of the tag. When the tag and the reading device (also referred to as a reader) are close enough to effect the transfer of energy, the tag ASIC generates a coded signal that is transmitted to the reader via a magnetic coupling.
In systems of this type, for many applications, it is desirable to be able to magnetically couple a tag to a reader at a considerable distance and with different relative orientations. Prior to the present invention it was necessary to increase the transmit power of the reader in order to increase the effective range between the reader and the tag. Any increase in a transmit power level involves cost, reliability, and safety considerations. Also, radiated power levels are limited by regulation, which in turn limits the magnetic coupling range which can be achieved.
For certain applications, it is desirable for a reader to identify several portable tags simultaneously. However, real time transmission from a plurality of tags to the reader as in previous systems, resulted at times in interference between tags.
In light of the foregoing, there is a need for a method and system of powering a portable tag for transmitting coded information to a reader that overcomes one or more of the disadvantages of prior arrangements.